The present invention relates to a method of measuring the surface temperature of a metallic body and also to an apparatus for measuring the surface temperature of a metallic body. More particularly, the present invention is concerned with a method of and apparatus for measuring temperature, suited for the measurement of surface temperature of a metallic body heated to a temperature of about 500.degree. to 800.degree. C., such as steel sheet in continuous annealing furnace.
Typical conventional non-contact type methods for measuring the temperature of a hot metallic body employ a radiation pyrometer or an optical pyrometer capable of measuring the surface temperature of the metallic body through detection of heat energy radiated from the metallic body. In these known methods, however, the accuracy of the measurement is deteriorated by fluctuations of the emissivity of the metallic body as the measuring object. To avoid this, it has been attempted to determine the emissivity correctly by, for example, making use of a reference radiation. This determination of emissivity, however, requires much time inconveniently. Accurate measurement of the emissivity itself is materially impossible when the emissivity is as small as 0.1 to 0.2.